This invention relates generally to advertising, and in particular to storing and serving advertising impressions to web browsers accessing online systems.
Advertisers pay various online systems to present their advertisements (“ads”) to users of the online systems. For example, users access online systems having websites including space allocated for advertisements through web browsers, and advertisers may provide bids to an online for displaying ads associated with the advertisers. Advertisers often seek to present ads to users likely to be interested in their products or services and most likely to purchase the advertised products or services. Accordingly, if a particular user is likely to purchase an advertised product or service, an advertiser may increase the amount bid to the online system to increase the likelihood of an advertisement from the advertiser being presented to the user.
To identify users likely to interact with an ad or likely to purchase advertised products or services, advertisers and their partners often track, store, and analyze users' online activity. A user's online activity informs advertisers of the preferences and behaviors of that user. Various techniques may be used to obtain a user's online activity. For example, cookies stored and on the user's computer, web bugs such as tracking pixels and JAVASCRIPT® tags, and locally shared objects.
Online system users are typically unaware of advertiser tracking, so these users are often unaware of the information provided to advertisers. For example, online activity tracking frequently begins when a user visits a web site, with no explicit request for permission to track. Further, sophistication online activity tracking has become more sophisticated, allowing advertisers to learn more and more about users. This increase in tracking sophistication, coupled with users' lack of knowledge about tracking, increases privacy concerns.